Histology Of The Respiratory Tract

Question 1

Respiratory epithelium

Answer 1

The respiratory system is largely lines by a type of epithelium called the respiratory epithelium
This lines the tubular/conducting portion of the respiratory system

Regarded as a pseudostratified columnar Cilliated epithelium

-Rests on a basement membrane

-Above the basement membrane lies a single layer of epithelial cells. However the nuclei of these cells are present at different heights giving the false impression that more than one layer of cells is present, but all of these cells are in contact with basement membrane

Question 2

2 types of respiratory epithelium cells are present in respiratory epithelium

Answer 2

Most common are ciliated epithelial cells

Distributed amongst these ciliated epithelial cells is a population of mucus secreting goblet cells

Question 3

Function of the nose

Answer 3

Filter, Humidify, Warm the inspired air

Also the site of olfaction- smelling

Question 4

At the first part of nostrils (the bit where we can touch with our fingers)

Answer 4

This is lined by keratinising, stratified squamous epithelium

Question 5

Further back, at the point where it becomes diffcult to touch

Answer 5

The mucosa changes to a non-keratinising stratified squamous epithelium

Question 6

Nasal cavity

Answer 6

This is lined by respiratory epithelium

The connective tissue underneath the respiratory epithelium comprise of loose fibrous connective tissue, containing a number of seromucinous glands (glands that produce catarrh/snot) and a rich network of blood vessels

Question 7

The nose- Olfaction

Answer 7

In the roof of the nasal cavity the epithelium is more specialised- olfactory epithelium

Olfactory epithelium is also a pseudostratified columnar ciliated epithelium but there is no goblet cells
The cillia are stereocillia- non motile

Contains basal epithelial cells but all cells are in contact with the basement membrane

Contains penetrating nerve fibres which all reach the surface of the epithelium

On the underlying connective tissue there is a rich network of serous glands of bowman. These secrete a watery fluid to help wash the surface clean
Large number of nerves in underlying connective tissue

Olfactory tissue lines only a small portion of the nose at the apex of the roof of the nose and extends a small distance into the septum and the lateral wall of the nasal cavity

Question 8

Olfactory receptors cells- bipolar neurones

Answer 8

Dendrite extends to surface to become club-shaped ciliated olfactory vesicle

Need silver stains to highlight the nerves

Question 9

The nasopharyngeal- further back into nose

Answer 9

Lined by respiratory epithelium

Function:
-Gas transport
-Humidification of inspired air
-Warming of inspired air
-Olfaction

Question 10

Nasal sinuses

Answer 10

Air filled spaces within the bones of the skull and facial skeleton

Function:
-to lower the weight of the frontal skull
-to add resonance to the voice
-Humidify and warm inspired air

Lined by respiratory epithelium

Question 11

The larynx

Answer 11

Cartilaginous box formed from almost entirely hyaline cartilage
Hyaline cartilage serve to hold the larynx open against negative pressure during inspiration

Site of voice production

Apart from the vocal cords, the inner aspect of the larynx is lined with respiratory epithelium

Question 12

The vocal cords

Answer 12

Function- Voice production

Reinke’s space- Stratified squamous epithelium overlying loose irregular fibrous tissue

Almost no lymphatics

Contains vocal ligament (not shown in image) comprises dense fibroelastic connective tissue
Beneath this is the vocalis muscle

Question 13

The trachea

Answer 13

Supported by hyaline cartilage arranged in a series of C shaped rings

Lined by respiratory epithelium

Function:
-Serves to conduct air to and from the lungs

Seromucinous glands in submucosa

C shaped cartilaginous rings are deficient posteriorly and the gap between the free ends of these rings is filled by a vertically orientated smooth muscle called trachealis

Trachealis muscle posteriorly

Question 14

The bronchi and bronchioles

Answer 14

Trachea branches at the carina to form the main bronchi

Then within he lungs these branch again to dorm the lobar bronchi, then again to form the segmental bronchi, then again into a number of different bronchioles

All bronchi contain
smooth muscle, partial cartilaginous rings, respiratory epithelium, some basal neuroendocrine cells, seromucinous glands and goblet cells

Bronchioles have different histological appearance
-Do not contain partial cartilaginous rings, respiratory epithelium (this becomes simplified to ciliated columnar epithelium)
-Have smooth muscle, some basal neuroendocrine cells
- Contain few goblet cells. Most goblet cells replaced by Clara cells

Question 15

Clara cells

Answer 15

Most numerous in terminal bronchioles- last part of the conducting airways

Roughly cuboidal
Pale staining cytoplasm, almost optically clear- vesicular cytoplasm

Mitochondria, smooth ER, secretory granules, no cilia;

Function (not completely certain):
-Secrete a lipoprotein that helps to prevent luminal collapse during exhalation- stops wall of bronchioles sticking together
-Role in oxidising inhaled toxins or in production of proteases to neutralise the effects of an inflammatory infection
-Role in removing surfactant in the lungs or are a stem cell population in lungs

Question 16

Respiratory bronchioles.

Answer 16

First part of distal respiratory tract

Function:
-Gas exchange
-Gas transport

Link the terminal bronchioles and alveolar ducts

Lined with cuboidal ciliated epithelium

Walls of the respiratory bronchioles contain spirally arranged smooth muscle
With no cartilage

Question 17

Alveoli

Answer 17

Site of gas exchange

150-400 million per lung

250 micrometer in diameter

Question 18

Alveoli cell types- Type I pneumocytes

Answer 18

Squamous epithelial cells, they are flattened

40% of cell population- small number of cells cover large area
90% of surface area of the alveolus

Contain few organelles as they aim to be as thin as possible as they are important in providing part of the blood, air barrier

Question 19

Alveoli cell types- Type II pneumocytes

Answer 19

60% of cell population
5-10% of surface area

Rounded cells
Round nucleus
Rich in mitochondria
Smooth and Rough ER

Produce surfactant- a protein which lowers surface tension in the lungs, making it easier to inflate the lungs

Question 20

Alveoli cell types- Alveolar macrophages

Answer 20

Phagocytic cell derived from blood monocytes

They are found in interstitial connective tissue of the alveolar walls and also within the lumen of the alveoli

Phagocytose particulates including dusts and bacteria that have reached the alveolar air spaces and have not been trapped by the mucociliary escalator of those parts of the respiratory trac- so they appear pigmented in people who have a lot of carbon in airways

Enter lymphatics or leave via mucocilary escalator

Question 21

Alveoli- blood-air barrier

Answer 21

Very thin

Comprises of type I pneumocystis lying on fused basement membrane of pneumoctyes and capillary that is shared with vascular endothelial cells

200-800nm thick

Question 22

Exam question: how many layers are there in the blood-air barrier?

Answer 22

3- type I pneumocyte, basement membrane and vascular endothelial cells

4- surfactant layer, type I pneumocyte, basement membrane and vascular endothelial cells

Divide it into more- surfactant layer outer cell membrane of the type I pneumocyte, type I pneumocyte’s cytoplasm, type I pneumocyte’s cell membrane, basement membrane, cell membrane of the vascular endothelial cell, cytoplasm of vascular endothelial cell,

Question 23

Alveoli- interstitium

Answer 23

This is where endothelial cells are not in direct contact with pneumocytes

Loose fibrous connective tissue comprising collagen and elastic fibres. Should be very little collagen and elastin in the walls of the alveoli

Contain fibroblasts, macrophages within walls of alveoli

Holes in walls of alveoli- Pores of Kohn
Help to equalise pressure between adjacent alveoli and help lungs inflate easily and evenly during inspiration
Allow infections to rapidly spread through lungs

Question 24

The visceral pleura

Answer 24

2 layers: one adherent to the outer surface if the lungs and one adherent to the inner surface of the chest wall

Flat mesothelial cells rest on a loose fibrocollagenous connective tissue

loose fibrocollagenous connective tissue has an irregular inner layer that is formed of elastic tissue, a layer of fibrous connective tissue in the middle and an outer irregular layer of elastic tissue